#7295: bad code for Double literals
------------------------------+---------------------------------------------
Reporter: jwlato | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.6.1 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: None/Unknown | Testcase:
Blockedby: | Blocking:
Related: |
------------------------------+---------------------------------------------
For this program
{{{
module Foo where
foo :: [Double] -> [Double]
foo = map f
where f x = x*(-0.5)
}}}
GHC generates the following core:
{{{
Foo.foo5 :: GHC.Integer.Type.Integer
[GblId,
Str=DmdType,
Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True,
ConLike=True, WorkFree=True, Expandable=True,
Guidance=IF_ARGS [] 100 0}]
Foo.foo5 = __integer 1
Foo.foo4 :: GHC.Integer.Type.Integer
[GblId,
Str=DmdType,
Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True,
ConLike=True, WorkFree=True, Expandable=True,
Guidance=IF_ARGS [] 100 0}]
Foo.foo4 = __integer 2
Foo.foo3 :: GHC.Types.Double
[GblId,
Str=DmdType,
Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=False,
ConLike=False, WorkFree=False, Expandable=False,
Guidance=IF_ARGS [] 51 20}]
Foo.foo3 =
case GHC.Float.$w$cfromRational Foo.foo5 Foo.foo4
of _ { GHC.Types.D# x_agI ->
GHC.Types.D# (GHC.Prim.negateDouble# x_agI)
}
Foo.foo1 :: GHC.Types.Double -> GHC.Types.Double
[GblId,
Arity=1,
Str=DmdType U(L)m,
Unf=Unf{Src=InlineStable, TopLvl=True, Arity=1, Value=True,
ConLike=True, WorkFree=True, Expandable=True,
Guidance=ALWAYS_IF(unsat_ok=True,boring_ok=False)
Tmpl= \ (eta_B1 [Occ=Once] :: GHC.Types.Double) ->
GHC.Float.timesDouble eta_B1 Foo.foo3}]
Foo.foo1 =
\ (eta_B1 :: GHC.Types.Double) ->
GHC.Float.timesDouble eta_B1 Foo.foo3
Foo.foo :: [GHC.Types.Double] -> [GHC.Types.Double]
[GblId,
Arity=1,
Str=DmdType,
Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True,
ConLike=True, WorkFree=True, Expandable=True,
Guidance=IF_ARGS [] 20 60}]
Foo.foo =
GHC.Base.map @ GHC.Types.Double @ GHC.Types.Double Foo.foo1
}}}
which looks pretty bad to me.
This may be related to #5731, especially as 'foo2 = map (* (-0.5))'
results in much better code.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7295>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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